I have a stand of 4 ponderosa pine trees. One has died, one is looking very sad and I have been watering it diligently once a week for the past 8 months and it is showing new growth. Now another one of the trees is turning brown at the upper branches. A local nursery said I should check for bugs. I put a piece of white paper under the branch and shook it and found one very tiny green bug that landed on the paper. Any thoughts on what is attacking my tree and what I can do about it? Picture attached